Disc drives incorporating head ramping devices are well known in the industry. Examples of this type of machine are disclosed in U.S. Pat. No. 4,535,374 (Amcodyne) and PCT Application Number US89/00785 (Prairietek). In each of these patents the read/write heads are attached to a gimbal device, which in turn is attached to a lead beam mounted to an actuator which moves the heads to the desired location on the disc surface. Prior to the application of power to the disc drive--and subsequent to the detection of a power loss--the heads are removed from engagement with the disc surfaces and suspended in their "parked" position by contact between the load beam and some sort of ramp or camming device located adjacent the outer diameter of the discs.
The read/write head of these types of devices typically consists of either an interrupted ferrite ring wrapped with wires for inducing or sensing magnetic flux variations in the disc surface, or an analogous arrangement created using thin-film deposition techniques. Whichever type of head is used, it is appropriately mounted to a "slider" which supports the head and allows attachment to the other elements of the system. For purposes of this discussion, the terms "head" and "slider" should be construed to refer to this head/slider subassembly unless specifically stated to the contrary.
In these prior art machines, the read/write heads "fly" on a thin layer of air called an "air bearing" which is created by the air frictionally dragged along by the spinning of the disc, acting in concert with co-operative flat surfaces on the bottom of the slider. These flat surfaces are referred to as "air bearing surfaces" or ABS.
The prior art gimbal of these assemblies has been further described in U.S. Pat. No. 4,176,765 and 3,931,641 (Watrous), and in U.S. Pat. No. 4,868,694 which is assigned to the assignee of the present invention. The gimbal is incorporated to compensate for small variations in the roll, pitch and skew of the read/write heads as assembled, and to create conformance between the surface of the spinning disc and the ABS of the "slider". To accomplish this task, the gimbal is made from very thin stainless steel, typically 0.0015 inches thick. This material is sufficiently strong to support the head during normal operation, and yet flexible enough to allow the necessary gimballing action.
With the current industry trend towards laptop and "notebook" computers, there has been a corresponding need to produce disc drives that are both incorporated in smaller packages and able to withstand the higher shock and vibration forces that are naturally to be expected when computers of this type are being carried from place to place. Computer manufacturers are beginning to demand that all sub-assemblies of their systems be able to withstand non-operating shock loads in the range of 300 Gs. A typical solution to the problem of large shock loads has been to ramp load and unload the heads, thus preventing "head slap" or potentially damaging contact between the heads and discs.
While ramp loading/unloading obviates the risk of damage due to head slap, such large shocks create another mode for potential failure.
When read/write heads are ramp-parked off the surface of the disc, the only material supporting the slider itself is the relatively weak gimbal. Shock loads of 300 Gs have been shown to be large enough to permanently deform the gimbal, resulting in the inoperability of the entire disc drive.